UPDATE
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This issue was caused by the compiler becoming buggy.
After a reboot, the problem disappeared.

However, I did find the definition for USERBUTTON was
wrong. It is set to 41, it should be 13.
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After struggling with IO problems using the Pinguino Micro Pic32, I soldered a LED board to see the I/O ouputs.
I found that the digitalRead( ) & digitalWrite( ) will not send a signal to pin #13. I have no knowledge of the Arduino and what may be necessary to attempt to make the PIC32 compatible but this seems to be a IDE bug since pins 10, 13, 20, and 28 also have multiple definitions.

It seems odd that the only way to write to this pin using digitalRead( ) & digitalWrite( ) is to use the pseudo pin #41 read/write. You can write/read normally using the connector P2_3 read/write.